You selected an automatic layout of the partitions. Your question in answered by the disklabel(8) man page, under "AUTOMATIC DISK ALLOCATION". There is a table that shows the partitions created and their minimum and maximum sizes.

Thanks J65nko ! Thanks jggimi !
Unfortunately I was in a hurry so I had done the fresh install before I read your posts but I will consider them in a future case.

I have a question please :
Is it better to create partitions that are being written much often (/var , .. , /tmp) before creating the rest (/usr/obj /usr/X11R6 ... ) ? would there be any inconvenience not following some 'assumed order' ( / --> swap --> /tmp --> /var --> etc )
Does skipping /dev/wd0f has any consequence ? I mean no f slice .. just e for /var and g for /usr .. etc .. I am asking this because I saw that an automatic disk allocation would use f for /usr ..

Is it better to create partitions that are being written much often (/var , .. , /tmp) before creating the rest (/usr/obj /usr/X11R6 ... ) ? would there be any inconvenience not following some 'assumed order'

There was a time when ordering partitions had performance benefits -- earlier partitions would be located on faster portions of the disk platters, but hard drive manufacturers today are only providing an interface which is compatible to legacy BIOSes. What is going on internally is anyone's guess -- especially when it comes to terabyte drives. So, any benefits which may have existed from using any particular partition ordering in the past are not necessarily still realized today.

I tend to use a specific partition ordering out of habit, but this is a practice which has marginal, if any, value anymore.